This disclosure relates to a sheet feeder, and more particularly concerns a sheet feeder with a fixed length, variable speed sheetpath for use with integrated electrophotographic printing machines.
In a typical electrophotographic printing process, a photoconductive member is charged to a substantially uniform potential so as to sensitize the surface thereof. The charged portion of the photoconductive member is exposed to a light image of an original document being reproduced. Exposure of the charged photoconductive member selectively dissipates the charges thereon in the irradiated areas. This records an electrostatic latent image on the photoconductive member corresponding to the informational areas contained within the original document. After the electrostatic latent image is recorded on the photoconductive member, the latent image is developed by bringing a developer material into contact therewith. Substantially, the developer material comprises toner particles adhering triboelectrically to carrier granules. The toner particles are attracted from the carrier granules to the latent image forming a toner powder image on the photoconductive member. The toner powder image is then transferred from the photoconductive member to a copy sheet. The toner particles are heated to permanently affix the powder image to the copy sheet.
In printing machines such as those described above, sheet feeders having a high capacity are utilized to supply sheets to the machine processor. Substantially these sheet stacks are supported on an elevator mechanism for supply to a fixed feedhead. The feedhead then forwards individual sheets along a fixed input path in a timed relation to the printing processor. These elevator mechanisms require a relatively high power motor to drive the sheet stack to the feedhead.
In other applications, a feeder device can be utilized wherein the sheet stack remains fixed and the feedhead moves as the sheet stack is depleted. However, when a feedhead is not fixed the length of the input path from the feedhead to the processor must be variable and the timing must then be corrected for the sheets as the path length changes. In this configuration, it can be desirable to have a variable length, variable speed sheetpath to maintain the proper timed relationship between sheets as the sheet stack is depleted.
The following disclosures may be relevant to various aspects of the present disclosure: U.S. Pat. No. 5,146,286 to patentee Rees et al., issued Sep. 8, 1992; U.S. Pat. No. 5,101,241 to patentee Watanabe, issued Mar. 31, 1992; and, U.S. Pat. No. 5,941,5.18 to patentee: Sokac et al., issued Aug. 24, 1999.
The relevant portions of the foregoing disclosures may be briefly summarized as follows:
U.S. Pat. No. 5,146,286 describes a device in which sheets are fed and stacked in the same device. A feeder having a fixed stacking tray is used with a floating feedhead in which the feedhead is connected to a stacking tray above the loading tray. As a sheet stack is depleted the finished sheets are discharged onto a stacking tray immediately above the sheet holding tray for an efficient use of space.
U.S. Pat. No. 5,101,241 discloses a sorter having an assortment of trays for receiving sheets. Sheets are directed to each tray by a moveable sheetpath from a processor to each tray.
U.S. Pat. No. 5,941,518 describes a device which includes a floating feedhead having a variable sheetpath for an electrophotographic printing machine. When the sheetpath is at its longest the feedhead and variable drive member operate at a higher speed to deliver the sheets to the sheet intake area at a predetermined time interval. As sheets are fed and the sheetpath becomes shorter, the variable drive and feedhead slow to maintain proper sheet timing. The sheetpath may also include a telescopic baffle configuration.